1. Field of the Invention
The present invention generally relates to a system and method for tracking the angular position of an engine's crankshaft.
2. Description of Related Art
Various systems for tracking the angle of an engine are known. Known systems determine the engine position from a sensor that generally works only above a minimum speed. These systems are based on a profile of the rotation of two engine position wheels, one on the crankshaft and one on the camshaft. In addition, at start-up these systems require the engine to initially rotate through an angle before the engine position becomes known. The amount of requisite angular displacement is dependent on the initial engine position.
It is desirable to know the engine position at engine startup, as this allows the system to fuel and ignite the very first possible cylinder. In the example of a port injected engine, the first possible cylinder would be the cylinder with an open or about to be opened intake valve. The benefits available from early ignition include minimization of tailpipe hydrocarbon emissions due to “crank-through” of fuel vapors from the intake manifold to the exhaust manifold, the minimization of crank time, and the reduction of crank time variability.
Typically, determination of engine position or engine tracking begins at engine crank and is not complete until some amount of engine rotation. The requisite rotation can slightly exceed two revolutions, depending on configuration. People have proposed systems that leave the controller powered after the engine off command and track the engine position until it comes to rest. However, known sensors have difficulty identifying engine reversals as the engine slows to a stop. Further, methods to detect the reversals are complex and can become unreliable in the presence of missing teeth on the position encoder wheel.
In view of the above, it is apparent that there exists a need for an improved engine position tracking system.